The present invention relates generally to navigational calculators and is more specifically concerned with a navigational calculator adapted to provide distance information relating to dogleg or zig-zag courses to a destination station.
The conditions of sea, current and wind are, singly or in combination, essential factors to be taken into consideration in the safe and efficient navigation of vessels. For instance, it is known that navigating a vessel directly into head seas tends to maximize the physical stresses to which the vessel and those aboard are subjected and, in the case of powerboats, often entails the use of increased motor speed (and fuel consumption) in order to overcome the slowing or stalling effect of the head seas acting against the hull of the vessel. In sufficiently severe head sea conditions it is often necessary to slow the vessel to the point of minimum headway in order to safely withstand the physical stresses imposed on the vessel and/or crew. It is also known that operations of a vessel in directly following seas can be troublesome, involving opportunities for broaching and/or pitchpoling of the vessel when it is overtaken by a wave or swell from astern. Thus, powerboat operations in a following sea often require continuous, expert and tiresome attention to throttle modulation in order to maintain the vessel in a safe position relative to the waves or swells. Additionally, in the case of sailboats, a directly
known to following wind of less than hull speed is known to result in less than maximum attainable speed of the vessel through the water.
In all of the foregoing instances, where the directions of the head or following seas and/or winds are essentially coaligned with the rhumb line or direct course to the destination station, a known and conventional navigational action is to take up a so-called "dogleg" or zig-zag course comprising a number of alternating course legs. The odd course legs are undertaken at a selected positive or negative relative angle to the rhumb line or direct course and the even course legs are undertaken at an equal, but opposite, relative angle to the rhumb line or direct course. These alternating and equal relative angles of the odd and even course legs are hereinafter collectively referred to as the "departure angle". Thus, the vessel is caused to criss-cross or contact the rhumb line course until the destination station has been reached. The dogleg course comprises only two course legs, the first departing from the rhumb line course while the second approaches the rhumb line course and intersects it at the destination station, the odd and even course legs thereby comprising the legs of an isosceles triangle, the base of which is defined by the rhumb line course. The zig-zag course, on the other hand, while similar in its basics to the dogleg course, comprises course legs whose number, in the aggregate, is greater than two.
By the dogleg or zig-zag course technique, the aforementioned problems of running directly into head or following seas and/or winds are usually substantially ameliorated and, in the case of sailboats whose rhumb line course would dictate running in a following wind of less than hull speed, the speed of the hull through the water is usually substantially increased over that achievable were the rhumb line or direct course to be navigated. Thus, while the dogleg or zig-zag course technique and its advantages are generally well known and understood to skilled mariners, the incremental distances to the destination station occasioned by use of this navigational technique are, practically speaking, rarely ascertained because, heretofore, the multiple trigonometric calculations and summations required to obtain this information have been relatively arduous and time consuming to perform. In accordance with the present invention, however, there is provided a novel navigational calculator in which this distance information, arising from the adoption of a dogleg or zig-zag course to a destination station, is readily and quickly obtainable as a function of the selected departure angle.
While there are, of course, many known navigational calculators, none is known to the present applicant which functions to quickly provide dogleg or zig-zag course distance information as a function of departure angle, as does the calculator of the present invention.